Wide-Range Epitaxial Strain Control of Electrical and Magnetic Properties in High-Quality SrRuO₃ Films

Abstract

Epitaxial strain in 4d ferromagnet SrRuO3 films is directly linked to the physical properties through the strong coupling between lattices, electrons, and spins. It provides an excellent opportunity to tune the functionalities of SrRuO3 in electronic and spintronic devices. However, a thorough understanding of the epitaxial strain effect in SrRuO3 has remained elusive due to the lack of systematic studies. This study demonstrates widerange epitaxial strain control of electrical and magnetic properties in high-quality SrRuO3 films. The epitaxial strain was imposed by cubic or pseudocubic perovskite substrates having a lattice mismatch of -1.6 to 2.3% with reference to bulk SrRuO3. The Poisson ratio, which describes the two orthogonal distortions due to the substrate clamping effect, is estimated to be 0.33. The Curie temperature (TC) and residual resistivity ratios of the series of films are higher than or comparable to the highest reported values for SrRuO3 on each substrate, confirming the high crystalline quality of the films. A TC of 169 K is achieved in a tensile-strained SrRuO3 film on the DyScO3 (110) substrate, which is the highest value ever reported for SrRuO3. The TC (146-169 K), magnetic anisotropy (perpendicular or in-plane magnetic easy axis), and metallic conduction (residual resistivity at 2 K of 2.10 -373 µΩ •cm) of SrRuO3 are widely controlled by epitaxial strain. These results provide guidelines to design SrRuO3-based heterostructures for device applications.

Bayesian optimization with experimental failure for high-throughput materials growth

“…The highest experimental RRR of 80.1, was achieved at the Ru flux = 0.365 Å/s, growth temperature = 826 °C, and O 3 -nozzle-to-substrate distance = 22 mm. This is the highest RRR ever reported among tensile-strained SrRuO 3 films 27,35 . The achievement of the target material with the highest conductivity in such a small number of optimizations demonstrates the effectiveness of this method utilizing the floor padding trick for high-throughput materials growth.…”

“…We demonstrate the effectiveness of the BO method with experimental failure first by using virtual data for simulation, and subsequently through implementation for real materials growth, namely machine-learning-assisted molecular beam epitaxy (ML-MBE) of itinerant ferromagnetic perovskite SrRuO 3 thin films, where we used the residual resistivity ratio (RRR) as the evaluation value. We achieved the RRR of 80.1, the highest ever reported among tensile-strained SrRuO 3 films, through the exploitation and exploration in a wide three-dimensional parameter space in only 35 MBE growth runs-the tensile-strained SrRuO 3 thin films achieved by epitaxial strain showed higher Curie temperature than those of bulk or compressive-strained films 27 . The proposed method provides a flexible optimization algorithm for a wide multi-dimensional parameter space that assumes experimental failure, and it will enhance the efficiency of high-throughput materials growth and autonomous materials growth.…”

“…5a). Rareearth scandate DyScO 3 has a GdFeO 3 structure, a distorted perovskite structure with the (110) face corresponding to the pseudocubic (001) face 27 . Since the in-plane lattice parameter for the pseudocubic (001) face of DyScO 3 (3.944 Å) is larger than that of bulk SrRuO 3 (3.93 Å), the SrRuO 3 films epitaxially grown on the DyScO 3 substrate is tensile strained.…”

Nanoscale Enhancement of the Local Optical Conductivity near Cracks in Metallic SrRuO3 Film

“…43−46 This general tendency might be understood crudely by a simple picture that the overlap between the free electron wave functions becomes reduced with a larger lattice constant. 22 To understand how the local infrared conductivity varies near a nanocrack, we obtain e xx and S 2 values for a given distance from the nanocrack. Then, we plot these values as open circles in Figure 6b.…”

Synthesis and electrical behavior of VO2 thin films grown on SrRuO3 electrode layers

“…In this study, VO 2 films were grown on conducting oxide SrRuO 3 (SRO) layers. Besides applications in magnetism, SRO is a widely studied template material to create multi-functional oxide heterostructures [34][35][36]. Furthermore, a recent simulation study has suggested that VO 2 /SRO bilayer heterostructures could be a promising candidate for relaxation oscillators [37].…”